In the semiconductor industry, embossing lithography methods are used increasingly to supplement or to replace standard optical lithography methods. By using microstructured and/or nanostructured embossing dies, a mechanical option of structuring viscous embossing materials, not limited to optical diffraction phenomena, is obtained. The structured, viscous embossing materials are cross-linked/hardened before and/or during the embossing process in order to remain dimensionally stable. In this case, the cross-linking is done in particular via electromagnetic radiation, preferably UV light, and/or by means of heat, i.e., thermally. After the cross-linking, the embossing die can be removed from the hardened embossing material. The remaining hardened embossing material either has a functional shape already or is further treated in subsequent process steps. A large amount of embossing material, primarily based on inorganic molecules, is heat-treated still at very high temperatures after the demolding step. The heat treatment ensures that the embossing material is irreversibly hardened. When using embossing materials with organic and inorganic molecules, the heat treatment primarily ensures that organic parts are removed from the embossing material and the inorganic molecules are cross-linked with one another. As a result, it is possible to structure an embossing material that is comprised of organic and inorganic molecules by die processes and to convert it after the die process into a completely inorganic material.
In order to carry out the structuring of the embossing material, special embossing dies are required. The embossing dies must meet extremely high requirements so that their micro- and/or nanometer-size structures can be transferred perfectly as negatives into the embossing material. In the state of the art, many different types of dies exist. A distinction is made in principle between hard and soft dies.
A hard die is comprised of metal, glass, or ceramic. It is less deformable, corrosion-resistant, wear-resistant, and very costly in production. The surface of the hard die is in most cases processed by electron beam lithography or laser beam lithography. These production methods are in general very expensive. The advantage of the hard die lies primarily in the high wear resistance. A decisive disadvantage exists in the high level of bending resistance, which does not allow the embossing die to be pulled off in pieces from the embossing material, as is possible in the case of soft dies. The hard die can be raised from the embossing material by a normal force only over its entire surface.
A soft die is very often formed as a negative of a hard die. In most cases, it is comprised of a polymer, and it has a high elasticity and a low bending strength. In most cases, it is entropy-elastic. The reason is primarily a high level of adhesion between the embossing material and the soft die and/or a swelling of the soft die. Soft dies can be distinguished from hard dies by various chemical, physical, and technical parameters. A distinction based on the elasticity property would be conceivable. Soft dies have a deformation property based primarily on entropy elasticity, and hard dies have a deformation property based primarily on energy elasticity. In addition, the two types of dies can be distinguished by, for example, their hardness. Hardness is the resistance that a material puts up against a penetrating body. Since hard dies are primarily comprised of metals or ceramics, they have correspondingly high hardness values. There are various ways of indicating the hardness of a solid. A very common method is the indication of the hardness according to Vickers. Without going into detail, it can be roughly stated that hard dies are to have Vickers hardness values of greater than 500 HV. Theoretically, such soft dies should be removable very simply from the embossing material, which is often not the case, however. The greatest problems with the current embossing techniques thus consist primarily in the demolding step, i.e., in the separation of the embossing die, in particular a soft die, from the embossing material.